1. Field of the Invention
The invention relates to a safety device for installation in lines for liquids, especially water, a beverage preparation device, with the pump delivering liquid into a container, and a device for delivering liquid, with a pump in a liquid line.
2. Description of the Prior Art
In a known beverage preparation device for preparing water containing carbon dioxide, "soda water," prepared or unprepared drinking water, but drinking water in particular, is raised to a high pressure by means of a pump and sprayed through a nozzle into a tank filled at least half way with carbon dioxide gas (CO.sub.2). The resultant water containing carbonic acid collects in the bottom half of the tank. Inside the tank there are two probes of different lengths, connected to a control device that switches the pump on and off. As soon as the liquid level reaches the shorter, upper probe, the pump is switched off. The water containing carbonic acid can escape through a drain cock located in the lower half of the tank. When the longer probe emerges from the surface of the liquid, the pump is switched on again after a brief delay of approximately 1 to 2 seconds. The pump again delivers water to the tank and the liquid level rises again until the upper probe is reached and the pump is switched off again.
The pump is the most sensitive part of this beverage preparation device, the pump frequently being a vane pump. For example if there is no longer any water in the line, the pump will run dry, causing it to break down relatively rapidly. To protect the vane pump against failure, the pressure is, for example measured, upstream and downstream of the pump. If the measured pressure differential does not reach a preset level, the control will switch off the pump. In addition, a heat sensor is mounted partly on the pump so that when a preset temperature is exceeded, the pump is also shut off. However, one disadvantage of this arrangement is that if the supply of drinking water is shut off because the level in the carbonic acid tank is too high, producing excessive pressure on the discharge side of the pump, i.e. the pressure differential between the input and output sides exceeds the preset level, the pump will deliver the water through its own pressure adjustment and overflow system in the circuit. Delivery into the tank is then no longer possible, however. In addition, in this device the pressure must be measured upstream and downstream of the pump. This is expensive since two pressure-measuring devices are required for the purpose, one upstream of the pump and the other downstream of the pump. In addition, a third measuring device is required for heat measurement.